1. Field of the Invention
The present invention relates to an ink-jet printing head and an ink-jet printing apparatus using same in which a vibrating plate constitutes a part of a pressure generating chamber communicating with a nozzle aperture for ejecting ink droplets, a piezoelectric element is provided via the vibrating plate and ink droplets are ejected by displacement of the piezoelectric element.
2. Description of the Related Art
For an ink-jet printing head for ejecting ink droplets from nozzle apertures wherein a vibrating plate constitutes a part of a pressure generating chamber communicating with a nozzle aperture for ejecting an ink droplet and ink in the pressure generating chamber is pressurized by deforming the vibrating plate by a piezoelectric element, there has been known a couple of types including one type in which a piezoelectric actuator in a longitudinal vibration mode which expands or contracts in the axial direction of a piezoelectric element is employed and the other type that employs a piezoelectric actuator in a flexural vibration mode.
For the former type, the volume of a pressure generating chamber can be varied by touching the end face of a piezoelectric element to a vibrating plate and a head suitable for high density printing can be manufactured. However, this type requires the use of a difficult process for cutting a piezoelectric element like the teeth of a comb with the piezoelectric element fitted to the pitch between nozzle apertures. Also, the positioning and fixing of the cut-out piezoelectric vibrator on a pressure generating chamber are required. Further, the manufacturing process is complicated.
On the other hand, for the latter, a green sheet formed of a piezoelectric material is formed in the shape of a pressure generating chamber and a piezoelectric element can be fixed on a vibrating plate in a relatively simple process in which the green sheet is burnt. However, since the flexural vibration is utilized, there would arise a problem that a large area is required and high density arrangement is difficult to achieve.
To solve the problem of the latter printing head, a method of forming a uniform piezoelectric material layer on the whole surface of a vibrating plate by a film forming technique and forming a piezoelectric element by cutting the piezoelectric material layer in a shape corresponding to a pressure generating chamber by lithography so that the cut piezoelectric material layer is independent of every pressure generating chamber is disclosed in Unexamined Japanese Patent Publication No. Hei. 5-286131.
This method is advantageous because it does not require a piezoelectric element to be stuck on a vibrating plate. Therefore, a piezoelectric element can be fixed by a precise and simple method called lithography and the piezoelectric layer can be formed so that it is thin and can be driven at high speed.
In this case, a piezoelectric element corresponding to each pressure generating chamber can be driven by providing at least an upper electrode for every pressure generating chamber with the piezoelectric material layer provided on the whole surface of the vibrating plate. However, it is desirable in view of the quantity of displacement per unit driving voltage and stress applied to the piezoelectric layer to provide in a part opposite to each pressure generating chamber and in a part crossing the outside a piezoelectric active part composed of the piezoelectric layer. Also, each upper electrode is provided in an area opposite to each pressure generating chamber, or at least a part except one end is formed within the area opposite to each pressure generating chamber.
However, when the piezoelectric active part in which an upper electrode pattern is formed on the piezoelectric layer is driven, a crack is readily made, particularly at the end of the piezoelectric active part and the piezoelectric active part may be fatally damaged.
If the end of the piezoelectric layer is designed to extend up to the peripheral wall of a pressure generating chamber, there is a problem that a crack is generated in a part opposite to the vicinity of a boundary between the pressure generating chamber and the peripheral wall.
These problems readily occur, particularly in a case where the piezoelectric material layer is formed by a film forming technique. The reason is that when the piezoelectric material layer formed by the film forming technique is very thin, the rigidity is lower, compared with that in case a piezoelectric element is stuck.